Expose information to extensions whether a build targets containers

[gunnarmorling]

See the discussion in #2794, there should be a way extensions can easily find out whether a build is targeting containers without having to query the native-image.container-runtime and native-image.docker-build system properties themselves.

[gsmet]

I'm not entirely sure if we have a way to do that now with the new stuff @stuartwdouglas worked on for the native image build.

@stuartwdouglas do you know off the top of your head if there is a way to do that now?

[stuartwdouglas]

You can inject io.quarkus.deployment.pkg.NativeConfig and look at the containerBuild field

[stuartwdouglas]

#5459 shows how this can be done